Recently, various commercial products such as electronic contents and various services are bought, sold, and provided through networks and various techniques are proposed for user authentication and security of communication. For example, a proposal has been made for a communication apparatus such as a facsimile apparatus capable of improving the security of a received document by effectively using a plurality of lines belonging to the apparatus (Japanese Patent Application Laid-Open Publication No. 2005-136940). A proposal has been made for a server device that allows the visual communication to be made at any place while achieving a sufficient security function for using telephones (Japanese Patent Application Laid-Open Publication No. 2006-339907). A proposal has been made for a data communication system capable of preventing an unauthorized access and easily recognizing an unauthorized access even when the unauthorized access is performed (Japanese Patent Application Laid-Open Publication No. 7-212353).